(a) Field of the Invention
The present invention relates to a system and method for controlling a power source of a hybrid vehicle. More particularly, the present invention relates to a method for controlling an engine and a motor which prevents excessive torque when a transmission malfunctions.
(b) Description of the Related Art
Hybrid vehicles use an engine as well as a motor (often an electric motor) as a power source to be able to reduce exhaust gas and improve fuel consumption efficiency, and as shown in FIG. 1, an engine 10, a motor 30, and an automatic transmission 40 are sequentially disposed along one axis in the hybrid vehicle, a clutch 20 is arranged between the engine 10 and the motor 30, and a torsion damper 50 is connected between the clutch 20 and the engine 10. Also, an integrated starter-generator is disposed to apply ignition torque for starting an engine 10, and an ISG (integrated starter-generator) 70 is connected to a crank pulley of the engine 10 through a belt pulley 75.
The hybrid vehicle uses the motor 30 in a low speed or at early take off stages when a vehicle starts moving to obtain a driving torque, because the efficiency of the motor 30 is better than that of the engine 10 at the early stages of the movement. However, after the vehicle starts moving, the ISG 70 ignites the engine 10 so that the engine 10 and the motor can be simultaneously used. As stated above, the hybrid vehicle runs based on generally an EV (electric vehicle) mode that uses only torque from the drive motor and an HEV (hybrid electric vehicle) mode that uses torque from the engine as a main power source and torque from the drive motor as a auxiliary power source to provide drive power to the hybrid vehicle. The EV mode is changed to the HEV mode by an engine starting through the ISG. That is, the hybrid vehicle uses at least two motors 30 and clutches 20 to improve power performance or fuel consumption efficiency and the outputted power is transferred to a drive shaft of a vehicle through the transmission 40.
Here, a shift lever is connected to a manual valve inside a transmission through a cable, gear shifting from the transmission 40 is detected thereby, and this physical gear information is transferred to a TCU (transmission control unit) by a gear shift step switch that is disposed on a shift lever. An intention of a driver is determined by a gear shift step of the transmission and then gear shift control is performed. If, however, there is no electrical signals for a gear shift step signal transferred to the TCU or several signals are inputted, it is determined that the TCU is broken or has malfunctioned and performs a control thereby.
For example, if it is determined that there is a problem with a switch for shifting a gear, R (reverse) is maintained in an R step of the transmission, a third speed is maintained in a D step of the transmission, a P/N step is maintained in a P/N speed, and when an accelerator pedal sensor (APS) is turned on in a P/N condition, the engine control system maintains the engine speed at 4500 rpm for a predetermined time and then operates an engine over-heating prevention logic to maintain the engine speed at 3000 rpm through an engine speed limitation control.
However, when the APS is turned on in a P/N condition of the transmission, the motor/engine speed is increased or revved to a required speed limit thereby utilizing unnecessary fuel and creating an uncomfortable situation for the driver and a potentially dangerous situation.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.